1. Field of the Invention
The present invention relates to switching circuits for controlling on-off switching of a power supply, and more particularly to a switching circuit for controlling on-off switching of a power supply for a CMOS (Complementary Metal Oxide Semiconductor) circuit.
2. Description of Related Art
Referring to FIG. 1, a typical switching circuit for a CMOS circuit includes a CMOS circuit 20′, a first resistor R1′, a second resistor R2′, a first capacitor C1′, a second capacitor C2′, a third capacitor C3′, and a switch 30′. The CMOS circuit 20′ includes a first circuit 50′ for storing the system time of a computer and a second circuit 70′ for storing other system settings of the computer. The switch 30′ includes three terminals 1, 2, and 3. An output terminal of a power supply 10′ is connected to the terminal 2 of the switch 30′ via the first resistor R1′. The terminal 3 of the switch 30′ is connected to ground. The terminal 2 of the switch 30′ is connected to ground via the first capacitor C1′. The terminal 2 is connected to a power input of the first circuit 50′. The power input of the first circuit 50′ is connected to ground via the second capacitor C2′. The terminal 2 is connected to a power input of the second circuit 70′ via the second resistor R2′. The power input of the second circuit 70′ is connected to ground via the third capacitor C3′. Generally, the switch 30′ is switched off and the CMOS circuit 20′ is powered on and used for storing the system time as well as system settings of the computer.
However, when the data stored in the CMOS circuit 20′ needs to be cleared, the terminal 2 of the switch 30′ is connected to the terminal 3, the switch 30′ is switched on. At this moment, both of the first circuit 50′ and the second circuit 70′ are grounded, so the data stored in CMOS circuit is cleared, as well as the system time.
Usually, when users reset the data stored in the CMOS circuit, they just need to set new system settings and do not need to reset the system time.
What is needed, therefore, is to provide a switching circuit for controlling on-off switching of a power supply for a CMOS circuit, that can keep the system time stored in the CMOS circuit when the switch is switched on.